1. Field of the Invention
The present invention is generally directed to the field of roofing materials and is more particularly directed to a method of making a molded roofing unit formed from a fiber-reinforced plastic.
2. Description of the Related Art
A number of different roofing products have been developed and used over the years to cover and protect a building. Various factors may be considered in choosing a roofing product including the cost of the product, ease of application or installation, and appearance. Equally important is the performance or weatherability of the roofing product, meaning its ability to withstand cold, rain, hail and wind and to shed snow and endure ice buildup without significant damage. Fire resistance is another important consideration and is increasingly being identified by insurance companies as a desirable attribute for lowering insurance premiums.
Clay tile, concrete, and slate roofs are distinctive and aesthetically pleasing in appearance such that even the "best" neighborhood associations approve the use of these roofing products. Clay, concrete, and slate also generally withstand wide ranging temperatures, rain, snow and wind, and are relatively fire resistant. However, these materials can be expensive, may be susceptible to damage from hail and foot traffic, and the installment is generally labor intensive. Further, slate, concrete, and clay roofing products can be heavy, such that reinforced structures may be required to support their weight.
Wood shakes are also generally approved by most neighborhood associations for residential use and are less expensive than clay, concrete, or slate roofs. Wood shakes are easier to install than clay, concrete, and slate roofs, although measuring and/or squaring of the individual shakes during installation can prove time consuming and the shakes may split during shipment or installation, thereby increasing the overall cost of materials. Wood shakes are also susceptible to hail damage and generally cannot attain a high degree of fire resistance without costly treatment. Wood shakes are often perceived as catching fire relatively easily in the presence of lightening, sparks from fireworks, or other airborne flames. When exposed to water, wood roofing materials may swell or curl along the edges, thereby providing a protruding surface for winds to catch.
Asphalt shingles, also known as composition roofing, are less expensive than wood roofing and are relatively easy-to-install. However, asphalt roofing products generally do not provide the sought after appearance of wood shakes, slate, clay, or tiles, and therefore are not approved for use in some residential areas with high-priced homes. While asphalt roofing is resistant to fire, it is generally prone to hail and wind damage and may need to be replaced over time due to brittling and cracking from exposure to the elements.
Due to the inadequacies of conventional roofing products, various attempts have been made in the past to develop plastic-based roofing materials that possess the desired combination of physical properties, low cost, aesthetic appeal and ease of installation.
For example, U.S. Pat. No. 5,635,125 to Ternes et al. discloses a relatively flat molded shingle formed of ground-up recycled polyvinyl chloride (PVC) particles and wood sawdust particles. U.S. Pat. No. 5,615,523 to Wells et al. discloses a relatively flat shingle panel comprising a resinous plastic material combined with a large amount of filler.
While these prior plastic and/or composite roofing products heretofore developed for replacing conventional roofing products are suitable for such purposes, none of the products developed to date have fully met the desires of the industry. These prior products do not provide the desired aesthetic attributes, nor superior physical properties. Thus, a need remains in the art for an improved plastic composite roofing product that may be made from relatively safe polyolefin materials, recycled and/or virgin, having high impact resistance, wind resistance and fire resistance, with an aesthetically pleasing appearance and that may serve as a drop-in replacement for traditional roofing products at a reasonable cost. To this end, one of the primary objects of this invention is to provide a polyolefin roofing unit reinforced by partially delignified fibers, in which the fibers bind to the plastic to provide a greater degree of wind resistance and impact resistance than previously known in plastic roofing products and with costs comparable to traditional roofing products.